1. Field of the Invention
The present invention concerns the graceful energization, and de-energization, of an electronic device, particularly a microprocessor-based digital electronic device, that is powered, typically with extremely small amounts of power obtained but slowly and erratically, by a low-level source of energy in the environment, particularly by such ambient light energy as is incident on the device.
2. Description of the Prior Art
2.1. The Preliminary Purposes and Operation of the Present Invention to which the Prior Art Must be Compared
The present invention will be seen to concern the accumulation of energy in an electronic device so that, after sufficient energy is accumulated, the electronic device may thereafter be operated at least periodically or occasionally. The energy available for accumulation is commonly (i) at very low levels, (ii) sporadic, and (iii) unreliable in amount over any period(s) of time ranging from seconds to months. The energy that is supplied to the electronic device at any one instant of time may potentially be at levels so low that the device would never be able to operate fully if it was to be dependent upon just this instantaneous supply of energy. Instead, the electronic device will typically be able to operate for the production of useful work, and to consume energy, only if, and when, energy has been accumulated over time periods longer than the device will be fully operative.
The present invention will be seen to particularly concern the graceful and correct initialization (or re-initialization) and energization of an electronic device, including computer microprocessors and computer memories. The device energizing an initializing device may start from a condition of absolutely no stored power. It my proceed, over one or more periods of time that may aggregate days and longer in length, to very gradually accumulate energy. The supply, and accumulation, of energy need neither be linear, nor even progressive. The energy supplied to the device may be, and typically is, parsimonious, irregular, and unreliable. It may never exceed an instantaneous magnitude that would ill serve to power a common digital wristwatch. The device accumulating this energy may have periods, including periods when it is not even operational for the conduct of useful work, when it energy stores actually diminish due to leakage and the like.
Nonetheless that an electronic device in accordance with the present invention will be seen to have to accumulate energy most diligently, and occasionally for very long periods, in order to accumulate sufficient energy for its (periodic, energy-conserving) operation, the device will be seen to do impressive amounts of useful work when actually (occasionally, periodically) operating. Moreover, the device always gracefully energizes to, and de-energizes from, its operational state.
If the device is able to store, or maintain, the smallest scintilla of energy then the work performed over multiple periods may be conducted in time sequence from one operational period to the next. Even if the device is deprived of any energy whatsoever for so long, and so profoundly, so as to, after the passage of sufficient time, have completely exhausted its reserves of stored energy (which energy reserves were likely minuscule to begin with), the device will nonetheless re-energize gracefully and, although devoid of knowledge of current real time, commence useful work. This useful work may, and normally does, include work that is scheduled to occur at fixed time intervals.
Particularly when powered from sources of energy in the environment--such as incident light energy--an electronic device in accordance with the present invention will be seen to have the interesting characteristic that, because it draws energy from its environment, the device need not be, and normally never is, shut off. The device will never be permanently stopped simply because, from time to time and at times, it receives no energy and/or has insufficient, or no, energy stored so as to operate.
The idea of a device that runs when it has energy, and that does not when it does not, is as simple as a common solar-powered calculator. However, a solar-powered calculator will not normally accrue energy to attain operability, and must be supplied with instantaneous energy in excess of its instantaneous consumption. Neither does a solar-powered calculator or like device commonly store energy by which it may, hopefully and if the magnitude of stored energy reserves permits, maintain track of real time from one period of operability to the next. Neither does a solar-powered calculator or like device commonly degrade gracefully--terminating present operations in an orderly and coherent manner while preserving, if useful, its present status and results--when it is deprived of power (or, should power be stored such as in batteries, when the stored power falls dangerously low). Of course, some microprocessor-powered "address books" do have a secondary battery to back up the primary battery, and maintain the integrity of information during replacement of the primary battery.
Electronic devices normally maintain the a coherence between their operations during temporally separated periods only so long as the devices are able to have at least some power, or to retain at least some power reserve(s). An electronic device in accordance with the present invention will be seen to cease, and to resume, operations at separated periods even when, between periods, it may be totally devoid of either supplied or (remaining) stored power. The inventors no of no comparable device so functioning.
2.2 Analogous Devices and Methods of the Prior Art--A Start-up from a Total Absence of Power and Energy
Further by analogy to the present invention, electrical and electronic devices and systems have previously been adapted to gracefully commence, or to suspend (or even cease), their operation dependent upon the adequacy of the electrical power that is instantaneously supplied to such devices or systems. The approaches previously employed by such devices or systems in response to degraded, or inadequate, electrical power range from the simple to the complex.
One, elementary, prior art approach is to simply suspend all functionality whatsoever during the persistence of no, or inadequate power. A more sophisticated approach, occasionally employed in military devices or systems where power outage or degradation is possible even while some coherence and integrity in device or system operation is desired to be maintained, is to store enough power to permit a graceful degradation of functionality upon even the most instantaneous and total interruption of power. Such devices and systems commonly also re-energize gracefully, and re-assume their full operational state, upon the restitution of adequate instantaneous power.
Electronic systems and devices that are sophisticated in response to the degradation or interruption of electrical power are normally not additionally burdened with having to account for the long-term adequacy in duration and in amount, as opposed to the instantaneous adequacy, of the electrical power that is supplied to the system or device. In other words, in the prior art supplied power is generally either sufficient--whether for some purposes or for all purposes of operation--or is insufficient for some, or for all, of these purposes. No consideration needs be, nor has, generally been given in prior art devices (or systems) as to whether such power as has already been supplied to the device (or system)--at certain levels and during certain time periods--has permitted the device (or system), to receive, and to store, a net total amount of electrical energy that is sufficient to now permit the device (or system) to continue, or to recommence, some, or all, of its operations. There is a particularly good reason why the energy history of the device (or system) is not commonly regarded when determining whether to commence, or re-commence, operations. Determination that power, and/or stored power, is adequate (or inadequate) for operation normally takes power. But if input power, and/or stored energy, is extremely low, just where is the power for evaluating the status of the power, or stored energy, to come from? Suppose that there is just enough power supplied, or energy stored, to determine just how little power (or stored energy) there is, and to determine that the device (or system) should not commence operation. What holds off the rest of the device (or system) from operating or attempting to operate, and consuming power, if the determination circuitry so determines? Is it to be control signals? If so, how are these signals to be generated, and interpreted, if there is scant power or energy? If holding the device (or system) dormant is to be the function of the determination circuitry, then how is it that this circuitry is operative to hold off all other circuitry while such other circuitry is not detrimentally consuming power?
Military computers, among other electronic devices, routinely possess an "auto start" capability. To this extent the prior art does show how to commence operations "gracefully". Commonly input power is increasing reasonably rapidly, and reliably--such as when the device is connected to an active power bus. In such a case operations are typically commenced only after a predetermined time delay, such as may readily be accomplished by a resistive/capacitive circuit. But what if power cannot be guaranteed to increase over any predetermined period, howsoever long? And, as before, how is the process of assessing, and reassessing, the adequacy of supplied and/or stored power--which activity itself takes power--to be performed, and repetitively performed, when there is little, or no, power to be had?
Power, or energy, management in the prior art generally makes certain explicit or implicit assumptions about the existence, and the nature of the supply, of energy and power. When these assumptions are absent, or de minimis, then the management of energy and power in an electronic device may approach the bind of being required to manage power (or energy) when there is no power (or energy).
A system or device that occasionally (no matter how infrequently) instantaneously uses more power than the power with which it is instantaneously supplied (satisfying the deficit in instantaneously supplied power from stored energy reserves) obviously must be concerned with energy transfer, as well as with instantaneous power. If it were not so concerned then the system or device might commence to operate upon the presence of adequate instantaneous power, but without adequate stored energy reserves. If so operative without adequate energy reserves, the system or device might be placed in an illogical, and/or unsatisfactory, operational state upon any requirement to expend more power than was instantaneously received.
2.3 Analogous Devices and Methods of the Prior Art--A Start-up when Instantaneous Input Power is Less than the Power Instantaneously Required for Operation, and is Potentially Perpetually so Less
Still another set of challenges results when a system or device is required to operate in an adverse power environment. Adverse power environments result when one or more power sources to the electrical system are at times individually and/or collectively unavailable and/or inadequate to meet either the (i) instantaneous or (ii) sustaining power demands of the system. Commercially available devices and systems have not generally been called upon to operate in these power environments. Military devices and systems occasionally are so operative in adverse power environments, but the main approach has been on storing power so as to permit continuing device or system operation (with minimum degradation) while operational emphasis shifts to power restoration.
Power management in electronic systems operating in adverse power environments has generally relied on several strategies.
First, power may be stored, as and when it is available to the electronic system, in energy storage devices such as batteries or capacitors. The operating electronic system draws its power from the energy stored in such energy storage devices.
Second, the use of power may budgeted over periods of any duration ranging from momentary to continuous. The cumulative amount of electrical energy provided to the system must exceed, over all such protracted time intervals as the system is required to be operational, the operational energy requirements of the system plus any losses incurred in the energy storage.
A third alternative, and sometimes complementary, strategy is to simply minimize the energy requirements of the electronic system. Particularly in microprocessor-based digital electronic systems this is commonly accomplished by minimizing the on, or active, time of the microprocessor and its associated electronics. The microprocessor and its associated electronics are typically clocked in operation. If the clock signal is periodically removed and/or is supplied at a low rate--thus lowering the effective duty cycle of the useful work performed--then the amount of power consumed by the electronics is generally reduced. The reduction in consumed power is, however, not necessarily in an amount that is proportional to the reduction in duty cycle and the attendant reduction in useful work. This is because the electronics generally consume some energy even while in a standby, non-operational, mode.
All these prior art schemes break down when no energy input and output budget can be established because, quite simply, the presence of any input power whatsoever is never guaranteed. The necessary strategy of the electronic system must seemingly be to run when (adequate) stored power and energy is, or becomes, adequate to so run, and to lie dormant when such stored power and energy is not so adequate. But then we are back to the potential impasse. If it takes power to monitor power, and to predicate operations based thereon, then who is to say that the power monitoring will not, especially when but extremely sparse and low power is provided to the electronic equipment, itself use up the power reserve faster, or as fast, as it is being accrued? And how is power to be monitored when there is not power? And how may an electronic device come from a condition of a total absence of any received or stored power to a condition of operability if such process takes, instead of a predetermined time period (which is typically a few seconds in the prior art), an undetermined length of time which may be days, weeks, or months and longer in length?
One reason that such electronic devices, and power management schemes, are not believed to exist in the prior art is because few persons desire to own an electronic device that takes on month to turn on. However, the slowness with which a device may turned on says little about the useful work that it may accomplish once turned on. And there may be valid reasons that the electronic device cannot receive, nor reliably receive, much energy. For example, a light-energized irrigation controller is subject in its collection of light energy to latitude, site factors (in the sun or in the shade), weather (cloudy or sunny), seasons (under snow, leaves or water) and human intervention (covered with a workman's coat, or a bag). However, howsoever unreliable and variable the light energy, if the irrigation controller could somehow come from an un-energized condition (maybe as it comes from the factory box, or after a long winter) to an operative and energized condition based on its accrual of light energy, and if it could thereafter operate to control irrigation, then this function would be exceedingly useful.
2.4 Sparse and/or Sporadic Supply of Environmental Energy to an Electronic System
The present invention will also be seen to deal with a requirement to manage electrical energy in an electronic device wherein the requirement cannot be met by a straightforward application of the strategies of (i) storing energy, and (ii) minimizing the system's use of the stored energy. The energy management requirement addressed by the present invention characteristically arises in electronic systems that are not powered by any connection to a power grid, and which also, on the whole, do not connect to or depend on battery or other sources of electrical power that are directly substitutionary for a power grid.
Electronics systems of this order receive most, if not all, of the energy which they use in their operation from non-electrical, generally low level, sources of power. Such non-electrical low-level sources of power may be, for example, (i) radiant or light energy, (ii) thermal energy, (iii) pressure variations, or (iv) mechanical forces, such as forces of fluid flow, to which the system is exposed. An energy conversion system converts the energy within the non-electrical external sources of power into the electrical power that an electronics system requires for its substantial continuing operation by means such as solar cells, thermionic generators, and standard electrical generators.
In deriving operational energy from their surrounding environment such electronic systems enjoy an independence of external, non-local and non-environmental power sources. In this manner environmentally-powered electronics systems operate in a manner similar to, and with similar independence to the independence exhibited by, certain exotic, and generally expensive, environmentally-powered clocks. Namely, the clocks derive the (generally mechanical) energy of their operation only, and exclusively, from sources of energy that are present within the environment within which the clocks reside, and to which the clocks are exposed. Such clocks are typically powered by temperature, or by atmospheric pressure, changes in the environment of the clock. Environmentally-powered electronic systems desirably function commensurately, and require no source of energy, nor any energy, other than that obtainable from their immediate environment.
Environmentally-powered electronic systems must manage energy. They characteristically manage such (generally modest) energy as they do consume in a manner that is fundamentally equivalent to conventional, grid-powered electronic systems. This is true regardless of the voltage, amperage or wattage of the environmental source of electrical power--electricity being electricity regardless of its source or derivation. The energy management performed by such systems includes considerations, and strategies, going to component selection, power storage, and power budgeting.
However, the present invention will be seen to contemplate that an "energy" interface to external sources of energy, and the management of this interface, should be much, much different in an environmentally-powered electronic system than it is in conventionally-powered electronic system. A simplistic strategy of "suck up all the energy that the (environmentally-powered) system can get", "store this energy", and "use the stored, and produced, energy until it runs out" is not going to work well for an environmentally-powered electronics system, as is hereinafter explained.
This is because an electronics system powered by sources of energy in the environment--such as light energy--is characterized by (i) sporadic, inconstant, and/or uneven levels of power supply, coupled with (ii) a general paucity in the total amount (watt hours, or watt minutes, or watt seconds, or joules) of energy available.
The (i) sporadic, inconstant, and/or uneven levels of supplied power result because the environment from which power is derived is uncontrollable, uncontrolled, or poorly controlled--especially by the electronic system. The electronic system cannot say "Environment, give me more power"; it is lucky to get what power it can.
For example, electronic systems employing solar cells or generators to derive electrical energy from environmental radiation, thermal and/or mechanical forces often derive and receive electrical energy in a highly sporadic manner. The sun may not shine, ambient temperature may not change, ambient pressure may not change, or fluid may not flow. Even when electrical energy is being instantaneously derived from more than one source of energy present within the environment, the collective rates of such derivations may be extremely low.
The (ii) general paucity in the total amount of energy available to an environmentally-powered system (whether electronic or no) results because localized, particularized, or customized electrical generators of whatsoever nature are often expensive, space-consuming, weighty, and/or unreliable. Fuel cells, nuclear generators, and water- or wind-powered rotary generators are basically akin to batteries, and require a special environment wherein fuel, radionuclides, moving water, or wind are present. The most common, and universally prevalent, ambient environmental energy sources on the planet's surface are (i) light, (ii) ambient temperature changes, and (iii) ambient atmospheric pressure changes.
Devices to extract power from these common ambient environmental energy sources have a volumetric density of power production that is several orders of magnitude worse than is the volumetric density of power consumption in and by common digital electronics. In other words, a generator powered by light, or by ambient temperature changes, or by ambient atmospheric pressure changes must typically be tens of cubic centimeters, or cubic meters, in volume in order to supply the energy consumption of a few cubic millimeters of electronic chips. Generators of reasonable, tens of cubic centimeters, volume that produce power either from light, from ambient temperature changes, or from ambient pressure changes characteristically produce electrical power (i) only sporadically, and then (ii) at milliwatt or lower power levels for (iii) intervals of hours or minutes. Accordingly, such generators characteristically produce only milliwatt hours or milliwatt minutes of energy within each diurnal period. Electrical and electronic systems that operate on such small amounts of electrical energy are called "micropowered".
The present invention will be seen to be concerned with power management in, and power management systems operative in, a power environment that is extremely adverse in terms of both (i) constancy and (ii) adequacy of power and energy production relative to consumption requirements. When the consumed power is, as is typical, environmentally derived in power converters having reasonable weight and volume, then the production, and necessarily the consumption, of power is correspondingly typically micropowered--typically at millijoule and lower energy levels.
2.5 Inconsistent, Sporadic, Unscheduled, and Unforeseeable Demands to Consume Electrical Energy
Nonetheless to the extreme adversity of such an environment of power production, the standard techniques of power budgeting, power storage, and minimizing power consumption might barely suffice, when applied at such extreme levels as would be required for satisfactory energy management, but that further complexities in the power management problem are present. These further complexities relate to power consumption as opposed to power production.
To momentarily skip ahead to ultimate point, the present invention will be further seen to also be concerned with a power environment that is adverse in its consumption, as well as (simultaneously) in its production of electrical power. An adverse power consumption environment is one where the use of power is (i) sporadic, inconstant, and/or uneven, and is (ii) occasionally very high relative to, or even greater than, either the magnitude of power that can be instantaneously produced from both generation and storage, and/or the energy that can be produced over certain time intervals from generation. The second, (ii), characteristics are particularly insidious: the demand for power and/or energy is not only irregular but may, by definition, outstrip any predetermined power or energy balance of the system. In the event that the system energy reserves are soon to be depleted, it is desirable that the system should degrade gracefully, and in an orderly manner.
Environmentally-powered electronic systems have previously generally been limited to those where instantaneous power is adequate to supply instantaneous consumption requirements. For example, the aforementioned solar-powered calculator will calculate only in the presence of energizing light regardless that the net energy balance of the calculator might be positive over a twenty-four hour or longer period. Even for those rare electronic systems, such a roadside emergency radio-telephones, that will work at one time (e.g., at night) from energy gathered at another time (e.g., from daylight), (i) a large, typically rechargeable battery, energy storage reservoir is maintained, while (ii) maximum power and/or energy drain is limited.
Variability in the amounts, times, and rates of power and energy received by an electronic system versus the amounts, times, and rates of power and energy expended necessarily constitute a continuum ranging from electronic systems wherein power management is trivial to those wherein it is impossible. Generally, however, no attempt at managing power from the environment in extremely small amounts has previously been made, regardless of net system energy balance over some useful period such as a day or a week, when both of two different complexities have been present.
The first complexity is a possible dearth of input power and energy for a sustained period. As already explained, this is common for environmentally-powered electronic systems.
The second complexity is the possible uncontrolled timing of a possibly significant power drain. This complexity is also common, typically arising when the system must use energy to communicate or to do unscheduled work.
The present invention will be seen to deal with the energy environment where, on average over some period, there may be energy enough, although possibly just barely enough, to perform useful work even though the instantaneous availability of adequate energy storage to meet an instantaneous power consumption is forever uncertain.
Upon initial consideration, the large number of variables postulated, and/or the extreme constraints encompassed might seem to present an impossibly difficult problem in energy management. Nonetheless to the difficulty of the problem of managing energy in the environment of the "real world", it would be useful if some progress could be made.
If electronic systems could "live" on power derived from the ambient environment in which they exist then they would exhibit a property of "life" other than (artificial) intelligence: such systems would obtain "sustenance" from their environment, much as do living organisms. Like living organisms--and unlike solar-powered clocks, watches, or calculators that perform set functions in a wooden, inflexible manner--such systems would be expected to use more energy at certain times in order to respond to sensed conditions and requirements. For example, a self-energized solar-powered irrigation control system might be expected to be able to "intelligently" control irrigation watering in accordance with sensed soil moisture conditions.
Interestingly, electronic systems that were capable of reliably deriving power from their environment, and that intelligently managed the power so derived, might, in accordance with the well-known longevity of digital electronic circuitry, effectively "live" for a very long time--much like a perpetual clock. Such environmentally-powered electronic systems might function nearly as long as the sun shone, the temperature changed, or the atmospheric pressure changed.
2.6 Still Further Problems of Power Management in an Adverse Power Environment
Meanwhile to the general problems of power management in an adverse power environment, there are at least two other particular problems--other than the general paucity, and randomness, of environmental energy sources and the lack of control in time and magnitude of energy consumption--that confront electronic systems attempting to operate substantially only from non-electrical energy sources within the environment of such electronic circuits.
A first problem--dealt with by the present invention--involves the graceful start up, and graceful degradation (if necessary) of the operation of the electronic system. If the electronic system is initially placed into the environment totally without any stored energy, and if its instantaneous average operational power consumption immediately exceeds the instantaneous average power that may be derived by conversion from non-electrical sources of power within the environment, then the system cannot accumulate any positive energy balance, and will perpetually remain in a nonoperative, dysfunctional, state.
By definition, if the electronic system is to derive operational power over protracted periods of time solely from converting a non-electrical source(s) of energy that are present within the environment of such system into electrical power, then the net power inflow from this (these) energy source(s) within the environment, after inefficiencies of conversion, must be greater than the average power consumption of the electronic system. However, these energy balances may be very close. Accordingly, an electronics system that is not specially controlled to start, or "come alive", gracefully within a degraded power environment may undesirably languish many hours, days, or weeks before sufficient power is accumulated so as to permit the electronic system to accomplish that processing for which it is designed and tasked.
As a specific example, consider if an irrigation controller was to be electrically energized by converting solar energy, or temperature changes, or pressure changes, or running water in the irrigation pipes that it controls, or some other ambient non-electrical source of energy into electrical power. Suppose that this environmentally-energized irrigation controller is taken out of its factory carton and installed. It must somehow accumulate sufficient energy so as to begin performing its irrigation control function(s) in an orderly, and timely, manner.
Alternatively, if, due to the insufficient provision of energy from environmental sources, the electrical energy balance within an electronic system that is dependent upon such environmental energy sources falls below a certain level, then the electronic system should degrade, suspend or cease its operations in a graceful and controlled manner.
As a specific example, again consider the hypothetical environmentally-energized irrigation controller. If its solar array were to be covered, or if the ambient temperature or pressure did not change, or if the irrigation pipes were to run dry, then it is certainly possible that the irrigation controller would run out of energy. It is of course, desirable that the irrigation controller should not choose to "die" for lack of energy while it has one or more irrigation valves turned on, and running water.
A second, and more subtle, problem facing electronic system that must operate in an environment of sparse, and sporadic, power input is due to possible asynchronous demands upon such electronic systems to "come alive", and to operate at a relatively high, or continuous, duty cycles in order to perform significant work. An electronic system may be asynchronously, and randomly, called upon to perform the selfsame processing that it might otherwise periodically, and regularly at long intervals, accomplish. If the electronics system is energy-budgeted for accomplishing its processing only periodically at intervals, then a problem arises only when the system is called upon to (i) perform the processing for more repetitions than its budget permits, or (ii) to re-perform the processing so soon after a scheduled processing that insufficient energy has been accumulated from the sporadic environmental sources of energy.
Another typical asynchronous demand upon an electronic system--which demand necessarily causes such electronic system to consume energy at a high rate--is a demand for communication. This asynchronous communication may transpire either by a communications channel to another electronic system, or by an operator interface to a human. When a human, in particular, wants to communicate with an electronic system then he/she cannot be expected to belay his/her request in consideration of the cumulative energy stored, or instantaneously available, to such electronic system. Neither can he/she be expected to prolong the duration of his communication only so long as the energy budget of the electronic system permits.
Both of these two eventualities--asynchronous demands on an electronic system to accomplish its normal function(s) in excess of the energy budget for such function(s) and asynchronous demands upon an electronic system to communicate--may be illustrated by the hypothetical example of an irrigation controller that derives its substantial operational energy from the environment within which it is located. Such operational energy might be derived, for example, by the conversion of incident sunlight into electrical energy. Such operational energy might alternatively be derived, for example, by a generator producing electricity in response to fluid flow within the irrigation watering system that is controlled by the irrigation controller.
The irrigation controller accumulates energy available from its environmental sources of energy, and performs its processing, and its control of irrigation valves, while operating under an energy budget. This energy budget is derived from the minimum energies that the irrigation controller may reliably extract from its environment.
If a human being asynchronously arrives at an irrigation controller then the human being may wish to (i) communicate with the controller, such as for purposes of programming its operations, and/or (ii) cause the controller to run trial, or test, irrigation sequences. Either of these two eventualities causes a severe energy drain on the stored energy of the irrigation controller. Even if the irrigation controller has stored significant electrical energy from its continuing conversion of non-electrical sources of energy present within its environment into electrical energy, and even if the irrigation controller has an immediate positive energy storage balance sufficient to perform the directed commands, it will not necessarily be reliably left with sufficient energy so as to continuously reliably perform the very irrigation control for which it is installed after completes (i) communication and/or (ii) test sequences with a human operator. Quite simply, a human operator that (i) communicates and/or (ii) tests a self-energized irrigation controller so as to pronounce it operative may, by the very act of (i) communication and/or (ii) testing leave the irrigation controller so bereft of stored energy that its subsequent failure is inevitable.
If the problem of energy insufficiency upon, or after, an asynchronous demand upon an electronics circuit to increase its functionality, and to attendantly increase its energy consumption, is to be satisfied then, by definition and by default, either (i) additional energy must be stored, or (ii) additional energy must be supplied to the electronic circuit. Previous electronics energy management systems do not resolve the question of where this (extra) energy should come from, and/or when it should be stored or provided.
As a further and alternative example of the complex, multi-faceted, energy environment within which modern electronics systems are operative, consider electronics equipments within a hospital. It is of great benefit to (i) safety, (ii) immunity to power reductions or outages, and (iii) transportability of hospital electronics equipments if they are not even connected to wall power, and are instead, insofar as is possible, self-contained--providing power for their own operation.
Modern micropowered and microminiaturized electronics may perform many useful monitoring and control functions in the hospital environment within minute energy utilization budgets. These minute energy budgets can readily be met by batteries. However, battery-powered electronic machines are extremely undesirable in the hospital environment because (i) they require a rigorous maintenance schedule for periodic replacement of the batteries, and because (ii) severe, life-threatening, consequences may result from hospital equipment unavailability due to the draining, or failure, of its battery power supply.
Hospital electronics equipments that are not connected to wall power might be energized, alternatively to the use of batteries, by small solar collectors. These solar collectors would convert the significant light energy present in the hospital environment into electrical energy used by the electronics equipments in performance of their prescribed function(s). Normally, however, the instantaneous rate at which electrical power can be converted from light energy that is incident upon a solar collector of reasonable size is very small. This small power is sufficient to power the monitoring and control functions of the hospital electronic equipment. However, the small instantaneous rate of electrical power production is manifestly insufficient to power an asynchronous, and irregular, demands that are made upon the electronic equipment, such as demands for operator communication.
Recalling the example of the irrigation controller, it is not desirable to attempt to meet asynchronous demands for increased energy consumption in and by a hospital electronic equipment by the storage of electrical energy. Any asynchronous demands might only then serve to deplete the energy store. A hospital electronic equipment that was left with an inadequate instantaneous energy storage balance so as to reliably perform its prescribed function(s) for a predetermined future period of time, even should no further energy be received, would be both undesirable and potentially dangerous. Accordingly, if reliably operative hospital equipments are to be powered by light or by some other source of power within the equipment environment, then their energy must be managed in a sophisticated manner to account for the many vagaries of both energy supply and energy use in the environment of such equipments.
The present invention will be seen to deal with energy management in a complex and adverse energy environment where energy, both electrical and non-electrical, is sporadically and parsimoniously supplied to an electronic system, and where the electronic system is called upon, sometimes sporadically and asynchronously, to expend energy at different rates for different purposes. The purpose of the present invention will be to manage energy for and within an electronic system (of a readily-available and readily-constructed type) sufficiently well so as to permit the electronic system to function normally, and operationally, and productively within an energy environment that provides only sparse and sporadic non-electrical sources of energy to the electronic system. This will be true even though the electronic system will accept and accommodate asynchronous demands that it should expend energy at a much greater rate and/or for a much longer time than can be accounted for by any reasonable energy budget based on a reasonable collection the environmental sources of non-electrical energy. In other words, energy management in accordance with the present invention will be directed to keeping an electronic system "alive" and reliably functional in the real world even though the real world is stingy, unreliable, and sporadic in its supply of energy while being capricious in its demands for such function(s) as the electronic system performs (with an attendant consumption of energy).
2.7 Irrigation Controllers and Valves would Desirably be Powered from their Environment
Almost all existing irrigation systems are a.c. powered. Use of a.c. power increases the cost of installing both the controllers themselves and the hydraulic components of the irrigation system as well. Traditional controllers are normally either wall mounted--normally on an internal or external wall of a building--or else are pedestal mounted in the landscape. Wall mounted controllers offer the convenience of being located in a central location where there is a.c. power available. However, this central controller location often necessitates the costly installation of long wire runs to bring the required low-voltage wiring from the controller to the valves. Controllers are often specified to reduce the cost of installing wiring to the valves, but a trade-off exists in that the cost of trenching and laying a.c. conduit to supply power to these controllers can be high. In addition, the pedestals alone are expensive. In either case, extensive wiring underneath pavement or heavily used areas is costly to install, repair, replace, or extend to new landscape areas.
Many municipal ordinances require temporary irrigation, before building construction can begin, to stabilize newly graded slopes. Temporary a.c. power has to be installed at considerable cost just to supply power to the irrigation controllers, often long before the actual building development begins.
There are reliability problems associated with dependence on a.c. power. Existing irrigation control systems are often sensitive to power supply disruptions and line spikes. Power outages typically cause a.c. powered controllers to revert to default "backup" programs, and necessitate professional attention to reprogram the controllers. Line spikes and surges can also disrupt or even completely destroy controllers. To protect controllers from line spikes, expensive power conditioning equipment is often specified by designers of irrigation controllers. Effective protection can cost almost as much as the controller itself. Because irrigation controllers are often distributed and wired over broad landscape areas they are frequently effected by line spikes caused by electromagnetic pulse or electrostatic discharge due to lightning.
An additional problem with existing controllers and common twenty-four volt alternating current (24 v.a.c.) valves is that the buried control wires are "ground referenced" and tend to pick up large "ground currents", particularly near power transmission lines. These induced currents have basically the same damaging effects as a.c. power line spikes.
The regulatory environment for the a.c. wiring of irrigation control is tightening. The National Electric Code requires any electrical wiring which is connected to a.c. power mains, and which might come into contact with water or plumbing, to be restricted to 15 volts or less. Presently, nearly all solenoid actuated diaphragm valves operate on 24 volts, so that existing equipment does not comply with this standard. Furthermore, changing to 12 volt solenoids would require more than twice the current to operate valves and hence would demand heavier, more costly, wiring and other components.
The cost of labor and materials in wiring a.c. power to the controllers of an irrigation system is a considerable portion of the overall system cost. For the example of an integrated multi-station irrigation control system for a large residential complex the wiring costs might amount to about 63% of total irrigation system installation cost.
If the irrigation controllers were self-energized, and did not require a.c. power, then they could be located closer to the valves, and the length of low voltage wiring from the dispersed self-energized controllers to the valves would be much reduced. The contractor's wiring costs for the same installation might then be reduced by up to 85%. There is thus a very great cost savings if a.c. wiring could be eliminated in an irrigation control system. If the costs of controllers and valves remained the same (which is by no means certain) then the overall irrigation system installation cost might decrease by up to 54% (i.e., 63%.times.85%).
2.7.1 Irrigation Controllers and Valves Typically Require a Remote, Alternating Current, Supply of Power because of their Energy and Power Use
A typical solenoid-actuated diaphragm valve, of which many tens or hundreds are typically used in an irrigation system, draws about 0.25 ampere continuous current at 24 v.a.c., or continuously dissipates about 6 watts. These solenoid-actuated valves are driven by electronic or electromechanical controllers. Because of the heavy power consumption of the solenoids, these systems are typically connected to a.c. power.
Latching solenoid-actuated diaphragm valves are available that draw current for a lesser time duration only upon opening and closing (latching and unlatching). Although these latching solenoid valves are generally more expensive, more complex, and more failure prone, they do reduce total system energy requirements. However, an irrigation system using latching solenoid valves still typically requires about 6 watts instantaneous power upon each occasion of a valve actuation.
An electronic irrigation controller of the type typically used in an irrigation system to typically control a number of irrigation stations or valves typically continuously dissipates about 0.5 amperes current at 120 v.a.c., or 60 watts. The power requirements of an efficient, modern, irrigation control system having a controller and eight typical solenoid valves will thus be recognized to be on the order of 66 watts when driving a valve.
Although a 24 hour per day 365 day per year usage of between 60 and 66 watts electrical power is not an insignificant cost in operating an irrigation system, it is the initial installation costs of an a.c. powered versus a self-energized irrigation system that is a primary problem helped by an environmentally-powered irrigation controller using an energy management system in accordance with the present invention.
Technological problems exist in realizing a self-energized irrigation system that alleviates any need for the remote supply of power, typically a.c. power. These problems have been discussed, and are recapitulated in the following section. To some extent these problems are a function of the power consumed in an irrigation system. Therefore it is useful to estimate the probable energy consumption of an irrigation system that could be constructed with existing technology so as to be very energy efficient. Typical low energy latching solenoid valves require about 24 vdc, 200 ma for 100 msec to change state. An irrigation controller constructed of low-power complementary Metal Oxide Semiconductor (CMOS), Medium Scale Integrated (MSI) and Large Scale Integrated (LSI) circuit technology might use about 200 chips. Such a low power irrigation controller might be built to consume less than 0.01 watts, or 240 milliwatt hours per day. On this power the controller would do sufficient calculation, and would execute an irrigation schedule, that would be sufficient to cycle one or more irrigation valves about 128 total times for all valves. Each of these valve cycles would consume about 480 milliwatt seconds or 0.13 milliwatt hours. The total 128 valve cycles would thus consume about 17 milliwatt hours. The energy budget for a very, very low power custom irrigation system would thus be on the order of 257 milliwatt hours per day, plus losses. This is on the order of 5000 times less than the 1440 watt hours that a conventional controller might use daily. It will be discussed in the following sections how difficult it is to meet even this modest energy budget.
2.7.2 Batteries Can Meet the Power and Energy Requirements for Irrigation Control Systems, but Present Problems
Batteries suffice to meet both the power and energy requirements of irrigation control systems. A battery has a low internal resistance, and can typically easily supply the 200 ma of current needed for a short time (about 100 msec) by a latching solenoid valve. The total energy consumption of energy-efficient irrigation systems may also be satisfied by batteries. At least one previous battery-powered irrigation controller exists in the market circa 1988. It uses four standard 6 volt lantern batteries.
Dry cell batteries have proven unreliable to meet the power demands of irrigation control. The battery is in an outdoor enclosure, and is subject to all prevailing climatic extremes of heat, cold, and humidity. The precise longevity of the battery, which is in part based on its intermittent power drain for controlling the switching of irrigation valves, is difficult to calculate. The batteries typically require replacement bimonthly or sooner. Even when often replaced (at considerable cost) the batteries are prone to deteriorate without warning to a condition inadequate to power the irrigation system. Because great damage to vegetation due to under-watering can quickly accrue, especially during hot weather, the failure of an irrigation system due to battery power failure is a highly detrimental occurrence.
2.7.3 Batteries Rechargeable by Solar Arrays can Power Irrigation Control Systems, but Present Problems
In response to the high expense, frequent periodic service requirement, and unreliability of using dry cell batteries to power irrigation control systems, at least one solar-powered irrigation control system has been attempted. Wet cell batteries that are approximately the size and power storage capacity of automotive batteries are used in the system. These batteries exhibit a significant charge leakage, or self-discharge rate, even if no energy is drained to power the irrigation control system. The batteries must power a typical irrigation controller that controls 8 latching solenoid valves that are collectively actuated up to 128 total cycles daily. In order to satisfy the leakage and consumed energy requirements a solar array of many square feet, typically at least six square feet (6 ft.sup.2), would be required to collect adequate solar power. A solar array this large is expensive, challenging to install and to guard against physical damage, and ungainly in appearance. It is unsuitable for most commercial and residential irrigation applications.
The wet cell batteries, although exhibiting a greater longevity than dry cell batteries, have a relatively short lifetime of months or years. They are expensive and cumbersome to replace. They may be unsafe in some applications where electrolyte leakage could be hazardous to plant or animal life.
2.7.4 Carbon Paste Electrode Electrolytic Capacitors can Store Appreciable Energy, but Cannot Discharge High Power Per Unit Time
Capacitors are a known means of storing electrical charge, or power. Relatively new high performance electrolytic capacitors based on carbon paste electrodes store large electrical charges. One such capacitor is the subject of U.S. Pat. No. 3,536,963.
These high performance, or "super", capacitors can be ranked as devices between a battery and a conventional capacitor. It is known to use these super capacitors as back up power sources in systems with microcomputers and/or CMOS memories.
Unfortunately, super capacitors are not practical to power conventional irrigation systems including controllers and valves. An array of many tens or hundreds of these super capacitors, each of which is relatively more expensive than a battery, would typically be required to store adequate power. An array this large exhibits significant leakage. Such leakage would require a similar, relatively large, solar energy collection array as would be required to keep wet cell batteries charged.
Finally, super capacitors have high equivalent series resistance (ESR), and are accordingly limited in the amount of power that each can deliver per unit time. Although considerate total power can be extracted from many tens, or hundreds of these super capacitors in a parallel array, just a few super capacitors are typically unable to provide adequate current flow so as to actuate a low-power latching solenoid valve.
These cost and electrical current limitations of super capacitors are not unique to their prospective use in rechargeable power sources for conventional irrigation systems. Although these super capacitors exhibit unique properties, their prior application in temporary backup power sources to digital logic devices has required that they should be initially charged by a device power supply that is typically a.c. powered.
2.8 No Matter what Kind of Energy Source is used for an Environmentally-Energized Irrigation System, the Source Incurs Severe Problems in According Sufficient Energy Storage Capacity so as to Accommodate Asynchronously-Occurring User Communication, and to Act Upon any Commands Resultant from this Communication
An energy source for a environmentally-energized irrigation system would normally be designed to supply all normal, quiescent, energy requirements of the system. If the energy source was to be sunshine, or light, then the energy collection and storage capacity should be sufficient to maintain the system in operation during periods of night, successive cloudy days, etc.
As previously explained in section 2.3, an environmentally-energized irrigation system must countenance the asynchronous arrival, night or day, of a user-maintainer of the system. The user-maintainer may proceed to communicate with the irrigation controller, cycle the irrigation valves, and/or initiate an irrigation schedule that may call for numerous immediate cycles of the valves. Each of these activities is individually difficult to budget and to satisfy with necessary energies. If the energy storage within an irrigation controller or system must power the communication of the system then it must store much more energy than would be needed for quiescent operation.
Yet asynchronously-occurring communication demands on an irrigation system by a user-maintainer are completely routine, and are to be expected. These demands place a great, essentially un-quantified and uncontrolled, demand on the energy storage capacity of any environmentally-energized irrigation system. Even when the system energy storage is of adequate capacity to meet these demands temporarily, as is normally the case with batteries, it is very common that a user-maintainer's communication with the system will seriously deplete or exhaust the energy storage of the system.
This is especially true if the user-maintainer exercises the system by causing cycling of the irrigation valves. All too commonly such an exercise and validation of an environmentally-energized irrigation system will so exhaust the power storage of the system so as to induce a power outage, and system failure, immediately or shortly after termination of the exercise and operational validation.
Still another problem occurs if the user-maintainer sets up a new irrigation control schedule. A rechargeable self-contained energy storage device, such as a battery recharged by solar power, may have exhausted its day's energy budget in performance of irrigation control and be awaiting recharge prior to again controlling the same diurnal cycle of irrigation. A user-maintainer may set up a new irrigation schedule, while the energy source device is depleted, that calls for an immediate energy drain. This energy drain will occur before the energy storage device may be, in due course, recharged. It is thus not sufficient that an environmentally-energized irrigation system should avoid unbudgeted energy losses during communication with, or exercise by, a maintainer-user. Rather, the system's energy source must be, for certain scenarios, left with more energy storage after communication than before!
Accordingly, no matter how energy-efficient an irrigation system is, and no matter how generously over-designed is its energy storage capacity, no environmentally-powered irrigation system is likely to store sufficient energy so as to permit that an unscheduled energy drain of significant magnitude may occur asynchronously with normal system power usage for the conduct of irrigation.